1. Field of the Invention
The invention relates to a vibration generator.
2. The Prior Art
In construction, vibration generators are used to introduce objects, for example profiles, into the ground, or to draw them from the ground, or also to compact ground material. The ground is excited by means of vibration, and thereby achieves a “pseudo-fluid” state. The goods to be driven in can then be pressed into the construction ground by a static top load. The vibration is characterized by a linear movement and is generated by rotating imbalances that run in opposite directions, in pairs, within a vibrator drive.
Vibration generators are vibration exciters having a linear effect, whose centrifugal force is generated by rotating imbalances. These vibration exciters move at a changeable speed. The size of the imbalance is also referred to as static moment. The progression of the speed of the linear vibration exciter corresponds to a periodically recurring function, particularly a sine function. On the basis of the sine-shaped progression of the force effect generated by the rotating imbalance masses, a drive that acts alternately in the forward drive direction and counter to it, with time offset, is produced. This effect is determined, in the final analysis, by static forces, particularly the inherent weight and static top loads. Without the superimposition of static forces on the vibration, the material being driven would not move forward, but rather simply vibrate back and forth.
The pile-driving process, with the aforementioned sine-shaped force progression, demonstrates significant energy consumption, which is additionally increased due to friction of the material being driven in the ground. The energy expended for the vibration generator brings about practically no forward drive. To eliminate this problem, it was proposed to couple multiple groups of imbalance masses that rotate at different speeds of rotation. The force progression of each imbalance group describes a sine curve. Addition of the individual force progressions, in total, yields a progression in which the amounts of the amplitude in the direction in which the forces are superimposed are greater than the amounts of the amplitudes in the opposite direction. This solution brings about a significant forward drive, thereby increasing the efficiency of the pile-driving process. However, the degree of efficiency is dependent on the speed of rotation required in each instance, on the mass of the goods being driven, on the construction method, and on the ground conditions. In order to be able to better utilize the available drive power and to limit the vibrations generated in the ground, a device is required that allows a simple change in the resulting static moment of at least one shaft group.